Working with list of pointer to structures in C.

test_ppstruct.c

#include <stdio.h>
#include <stdlib.h>

/* gcc test_ppstruct.c -o test_ppstruct -Wall */

struct point {
  double x;
  double y;
};


/* this is OK */
int point_init(struct point **pt, int i) {
  i++;
  *pt = malloc(sizeof(struct point));
  (*pt)->x = 10.0 * i;
  (*pt)->y = 11.0 * i;
  return 1;
}


/* this is OK */
int point_init2(struct point **pt, int i) {
  struct point *p;  /* easier to read code by avoiding long pointer names */
  i++;
  p = malloc(sizeof(struct point));  /* now points to good place in mem */
  p->x = 10.0 * i;
  p->y = 11.0 * i;

  *pt = p; /* copy the address of p to *pt. p should go out of scope then */
  return 1;
}


int main(int argc, char *argv[]) {

  struct point **points;
  size_t npoints = 2;
  size_t i = 0;


  points = malloc(npoints * sizeof(*points));

  for (i = 0; i < npoints; i++) {
    // point_init(&points[i], (int) i);
    point_init2(&points[i], (int) i);
    printf("%li %f %f\n", i, points[i]->x, points[i]->y);
  }

  /* now free it properly */
  for (i = 0; i < npoints; i++) {
    free(points[i]);
  }
  free(points);

  /* valgrind happy */
  return 0;
}